Model Comparison

GPT-4o vs Grok-4 Fast ReasoningWhich is better in 2026?

Comparing GPT-4o and Grok-4 Fast Reasoning across benchmarks, pricing, and capabilities.

Verdict: GPT-4o vs Grok-4 Fast Reasoning — which is better?

GPT-4o (by OpenAI) and Grok-4 Fast Reasoning (by xAI) are two of the AI models people compare most. Here is how they stack up on benchmarks, price and capabilities, and which one to pick in 2026.

On price, Grok-4 Fast Reasoning is roughly 15.9x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

Grok-4 Fast Reasoning also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.

Choose GPT-4o if…

  • you want predictable pricing at $2.50/M input and $10.00/M output

Choose Grok-4 Fast Reasoning if…

  • cost matters — it's about 15.9x cheaper per token
  • you process long inputs — it offers a 2,000,000 token context window
  • you want the most recent training data — it shipped Aug 2025
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Performance Benchmarks

Comparative analysis across standard metrics

No common benchmarks found

GPT-4o and Grok-4 Fast Reasoningdon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

Grok-4 Fast Reasoning costs less

For input processing, GPT-4o ($2.50/1M tokens) is 12.5x more expensive than Grok-4 Fast Reasoning ($0.20/1M tokens).

For output processing, GPT-4o ($10.00/1M tokens) is 20.0x more expensive than Grok-4 Fast Reasoning ($0.50/1M tokens).

In conclusion, GPT-4o is more expensive than Grok-4 Fast Reasoning.*

* Using a 3:1 ratio of input to output tokens

Lowest available price from all providers
Mon Jun 15 2026 • llm-stats.com
OpenAI
GPT-4o
Input tokens$2.50
Output tokens$10.00
Best providerAzure
xAI
Grok-4 Fast Reasoning
Input tokens$0.20
Output tokens$0.50
Best providerxAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Grok-4 Fast Reasoning accepts 2,000,000 input tokens compared to GPT-4o's 128,000 tokens. Grok-4 Fast Reasoning can generate longer responses up to 30,000 tokens, while GPT-4o is limited to 4,096 tokens.

OpenAI
GPT-4o
Input128,000 tokens
Output4,096 tokens
xAI
Grok-4 Fast Reasoning
Input2,000,000 tokens
Output30,000 tokens
Mon Jun 15 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Both GPT-4o and Grok-4 Fast Reasoning support multimodal inputs.

They are both capable of processing various types of data, offering versatility in application.

GPT-4o

Text
Images
Audio
Video

Grok-4 Fast Reasoning

Text
Images
Audio
Video

License

Usage and distribution terms

Both models are licensed under proprietary licenses.

Both models have usage restrictions defined by their respective organizations.

GPT-4o

Proprietary

Closed source

Grok-4 Fast Reasoning

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-4o was released on 2024-05-13, while Grok-4 Fast Reasoning was released on 2025-08-28.

Grok-4 Fast Reasoning is 16 months newer than GPT-4o.

GPT-4o

May 13, 2024

2.1 years ago

Grok-4 Fast Reasoning

Aug 28, 2025

9 months ago

1.3yr newer

Knowledge Cutoff

When training data ends

Neither model specifies a knowledge cutoff date.

Unable to compare the recency of their training data.

No cutoff dates available

Provider Availability

GPT-4o is available from Azure, OpenAI. Grok-4 Fast Reasoning is available from xAI.

GPT-4o

azure logo
Azure
Input Price:Input: $2.50/1MOutput Price:Output: $10.00/1M
openai logo
OpenAI
Input Price:Input: $2.50/1MOutput Price:Output: $10.00/1M

Grok-4 Fast Reasoning

xai logo
xAI
Input Price:Input: $0.20/1MOutput Price:Output: $0.50/1M
* Prices shown are per million tokens

Outputs Comparison

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Key Takeaways

OpenAI

No standout differentiators in the data we have for this pair.

xAI
Larger context window (2,000,000 tokens)
Less expensive input tokens
Less expensive output tokens
OpenAIGPT-4o
xAIGrok-4 Fast Reasoning
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Detailed Comparison

AI Model Comparison Table
Feature
OpenAI
GPT-4o
xAI
Grok-4 Fast Reasoning

FAQ

Common questions about GPT-4o vs Grok-4 Fast Reasoning.

Which is better, GPT-4o or Grok-4 Fast Reasoning?

GPT-4o (OpenAI) and Grok-4 Fast Reasoning (xAI) each have strengths in different areas. Compare their benchmark scores, pricing, context windows, and capabilities above to determine which fits your needs.

How does GPT-4o compare to Grok-4 Fast Reasoning in benchmarks?

GPT-4o scores MGSM: 90.5%, HumanEval: 90.2%, MMLU: 88.7%, DROP: 83.4%, MATH: 76.6%.

Is GPT-4o cheaper than Grok-4 Fast Reasoning?

Grok-4 Fast Reasoning is 12.5x cheaper for input tokens. GPT-4o costs $2.50/M input and $10.00/M output via azure. Grok-4 Fast Reasoning costs $0.20/M input and $0.50/M output via xai.

What are the context window sizes for GPT-4o and Grok-4 Fast Reasoning?

GPT-4o supports 128K tokens and Grok-4 Fast Reasoning supports 2.0M tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-4o and Grok-4 Fast Reasoning?

Key differences include context window (128K vs 2.0M), input pricing ($2.50 vs $0.20/M). See the full comparison above for benchmark-by-benchmark results.

Who makes GPT-4o and Grok-4 Fast Reasoning?

GPT-4o is developed by OpenAI and Grok-4 Fast Reasoning is developed by xAI.

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